1. Technical Field of the Invention
The present invention relates to cellular telephone networks and, in particular, to the network passing and handling of transmitted international mobile station identity (IMSI) numbers during authentication and registration, call delivery and call hand-off.
2. Description of Related Art
Perhaps the most important selling feature of cellular telephone service is the advantage of mobility. Those persons who subscribe to a cellular telephone service do so in order to be able to make and receive telephone calls without being tied to a fixed location. Such subscribers further often carry their cellular telephones with them on trips, and make use of their subscriptions while roaming not only within their home country, but also within foreign countries. It is when persons roam to different countries whose service is regulated by different standards and numbering plans, and provided using different protocols that conflicts and concerns with service provision often arise.
One instance of potential conflict arises when two or more cellular telephones are assigned use of the same mobile identification number (MIN), where the numbers are attributed to two different numbering plans, and where one of those telephones roams into the service jurisdiction of the other telephone. For example, in instances where a detection from the mobile station electronic serial number (ESN) of a fraudulent cellular telephone is not made, and if that roaming cellular telephone should make a registration within the visited service jurisdiction, the other (home) cellular telephone may be wrongly marked by the system as being located at the roaming telephone location. In such a case, an incoming call to the home telephone may instead be directed to the roaming cellular telephone. Furthermore, the subscriber profile for the home cellular telephone may be downloaded from the home location register to the switching center currently serving the roaming cellular telephone. The roamer accordingly has access to an incorrect profile. Also, charges for calls made or received by the roaming cellular telephone may be incorrectly billed to the account of the home cellular telephone. Other problems arising in such a situation are known to those skilled in the art.
Another instance of potential conflict arises when a cellular telephone roams into a service jurisdiction which does not recognize the numbering plan to which that mobile station's mobile identification number is associated. For example, in attempting to provide service to the cellular telephone, the cellular system may not be able to identify the home location register to which the telephone belongs. Accordingly, service to the cellular telephone may be denied, or somewhat limited (and potentially incorrect) service will be provided using a default subscriber profile.
Each of the foregoing instances of potential conflict arise because of problems encountered in attempting to uniquely identifying the cellular telephone requesting service. It is therefore of some concern that cellular telephones be uniquely identified on a world-wide basis, rather than just within one or more individual cellular service jurisdictions or numbering plans.
Some solutions have been proposed to this problem. For example, from the perspective of the air interface, the TIA/EIA IS-136A Specification provides for the assignment of a unique international mobile station identity (IMSI) number to each cellular telephone. With implementation of this identification scheme, every cellular telephone will have its own unique identification number. Responsive to the system information received in the overhead message train, the IS-136A mobile station uses either the mobile identification number or the international mobile station identity number to identify itself over the air interface. While IS-136 addresses the use and transmission of the international mobile station identity number over the air interface by a cellular telephone, there is no specification for how this number is to be processed by the cellular network in view of the existing use and registration of mobile identification numbers (MINs) for cellular telephones. Accordingly, there is a need then for a specification of the network operations (and in particular the operations of registration, authentication, call delivery and handoff) supporting the use of the international mobile station identity number as transmitted over the air interface.